Electrode Array and Method of Fabrication

ABSTRACT

An electrode array, having application as a cochlear implant, includes a tube formed of Parylene defining a hollow channel. A substrate formed primarily of Parylene is supported by the tube. In turn, a plurality of metallic electrodes and feed lines are supported by the substrate. Numerous voids are defined by the tube which opens into the hollow channel. The size and spacing of the voids regulate stiffness and curl of the tube to provide excellent fit within the cochlea.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant No.EEC-9986866 awarded by the National Science Foundation. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention relates to an array of electrodes. Specifically,the subject invention relates to an array of electrodes for use as partof a cochlear implant.

2. Description of the Related Art

Cochlear implants are the most widely used neural prostheses, usingcurrent stimulation to bypass the non-functional hair cells of thecochlea to directly stimulate receptor cells that drive the auditorynerve. Typical cochlear electrode arrays are fabricated with bundles ofwires coated in silicone. Such wire bundles are hand assembled and arelimited in the number of electrodes. A typical cochlear electrode arrayutilizes only 16 to 24 electrodes because of large size relative to thesize of the scala tympani. The low number of electrodes results in oftenpoor pitch specificity. The relatively large size of these electrodearrays may also cause insertion damage and limit the depth of insertion.The low insertion depth limits the pitch range provided by the implant.

The subject invention is directed toward providing an electrode arrayproviding greater pitch specificity, greater pitch range, whileresulting in minimal insertion damage.

SUMMARY OF THE INVENTION AND ADVANTAGES

The subject invention provides an electrode array. The electrode arrayincludes a tube having at least one wall wherein the tube defines achannel. A substrate comprised of a non-conductive material is supportedat least partially by the tube. The electrode includes a plurality ofelectrodes. Each electrode comprises a conductive material and issupported by the substrate. A plurality of feed lines comprised of aconductive material are disposed primarily within the substrate. Eachfeed line is electrically connected to at least one of the plurality ofelectrodes. At least one wall of the tube defines a plurality of voidsinto the hollow channel for regulating stiffness and curl of the tube.

The subject invention also provides a method of fabricating theelectrode array. The method includes the step of depositing a firstcomposition on a carrier wafer. The first composition defines alongitudinal slit and forms a first layer of the substrate. The carrierwafer is etched through the longitudinal slit to define a channelunderneath the first layer. The method also includes depositing a secondcomposition comprising a polymer through the longitudinal slit and ontothe carrier wafer to form the tube around the channel and seal thelongitudinal slit. The method further includes the step of disposing aplurality of feed lines comprised of conductive material on thesubstrate opposite the tube. The plurality of electrodes is disposed onthe substrate with each electrode electrically connected to at least oneof the feed lines. The method further includes the step of etching thecarrier wafer opposite the substrate to define voids with each voidexposing an area of the tube The areas of the tube exposed by the voidsare removed to define slots within the tube. The tube and substrate arethen released from the carrier wafer.

The electrode array provides a lower profile than those of the priorart, resulting in less damage when inserted into a cochlea. Theelectrode array also provides a greater number of electrodes and allowsfor deeper insertion into the cochlear, resulting in improved pitchspecificity and greater pitch range. Furthermore, the slots of the tubeof the electrode array assist in providing a modiolus-hugging curl toposition the electrodes as close as possible to the receptor cells andreduce insertion trauma.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a top view of an electrode array of the subject inventionshowing an interconnect region and thirty-two electrode sites in anelectrode region;

FIG. 2 is a widthwise cross sectional view of the electrode array duringfabrication showing a carrier wafer after a first layer of a substratehas been disposed atop;

FIG. 3 is a widthwise cross sectional view of the electrode array duringfabrication showing a longitudinal slit defined by the first layer;

FIG. 4 is a widthwise cross sectional view of the electrode array duringfabrication showing a carrier channel defined by the carrier waferunderneath the first layer;

FIG. 5 is a widthwise cross sectional view of the electrode array duringfabrication showing a tube and a second layer of the substrate;

FIG. 6 is a widthwise cross sectional view of the electrode array duringfabrication showing a feed line disposed on the second layer;

FIG. 7 is a widthwise cross sectional view of the electrode array duringfabrication showing a third layer of the substrate disposed on thesecond layer and the feed line;

FIG. 8 is a widthwise cross sectional view of the electrode array duringfabrication showing an electrode disposed above the third layer and incontact with the feed line;

FIG. 9 is a widthwise cross sectional view of the electrode array duringfabrication showing a fourth layer of the substrate disposed above thethird layer;

FIG. 10 is a lengthwise cross sectional view of a portion of theelectrode array during fabrication showing the fourth layer;

FIG. 11 is a widthwise cross sectional view of the electrode arrayduring fabrication showing a curl strip disposed above the fourth layer;

FIG. 12 is a widthwise cross sectional view of the electrode arrayduring fabrication showing a fifth layer of the substrate disposed abovethe curl strip and the fourth layer;

FIG. 13 is a widthwise cross sectional view of the electrode arrayduring fabrication showing a void disposed in the carrier wafer oppositethe substrate;

FIG. 14 is a lengthwise cross sectional view of a portion of theelectrode array during fabrication showing voids disposed in the carrierwafer opposite the substrate;

FIG. 15 is a lengthwise cross sectional view of a portion of theelectrode array during fabrication showing slots defined by the tube toexpose a tube channel;

FIG. 16 is a widthwise cross sectional view of the electrode array;

FIG. 17 is a lengthwise cross sectional view of a portion of theelectrode array;

FIG. 18 is a perspective view of a portion of the electrode array;

FIG. 19 is a close-up top view of a pair of electrodes of the electrodearray; and

FIG. 20 is a perspective view of a portion of the electrode array with awire disposed

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figures, wherein like numerals indicate like partsthroughout the several views, an electrode array 20 is shown herein. Theelectrode array 20 is well suited for use as part of a cochlear implant(not shown), but other uses of the electrode array 20 are describedfurther below and/or will be realized by those skilled in the art.

The electrode array 20 includes a substrate 22 at least partiallysupported by a tube 24. In the illustrated embodiments, the substrate 22and tube 24 each comprise a non-conductive material. Specifically, thesubstrate 22 and tube 24 of the illustrated embodiments each comprise apolymer and more specifically, the substrate 22 and tube 24 eachcomprises poly(p-xylene), known commonly by the trade name Parylene. Inthe illustrated embodiments, Parylene C is utilized to form thesubstrate 22 and tube 24. However, in other embodiments, other types ofParylene, other types of polymers, and other types of non-conductivematerials may alternatively be utilized to form the substrate 22 andtube 24. Furthermore, electrically conductive materials, such as metals,may alternatively be used to form the tube 24. Moreover, the substrate22 and tube 24 may be formed of a combination of different materials.

The electrode array 20 may include more than one tube 24 connected tothe substrate 22, i.e., a plurality of tubes 24. However, for purposesof illustrative simplicity, the electrode array 20 is shown anddescribed herein with only a single tube 24.

The tube 24 includes at least one wall 26, 28 of defining a hollowchannel 30 referred to hereafter as the tube channel 30. In theillustrated embodiment, the tube 24 has a generally semicircular crosssection defined by a curved wall 26 and a generally straight wall 28, asshown in FIG. 16. The generally straight wall 28 of the illustratedembodiment is connected to the substrate 22 as described in furtherdetail below. Other shapes for the tube 24 may be realized by thoseskilled in the art. Moreover, the use of the term “tube” does notnecessarily imply a circular or curved shape.

In one embodiment, the at least one wall 26, 28 of the tube 24 defines aplurality of slots 32 into the tube channel 30. Specifically, in theillustrated embodiments, the slots 32 are defined by the curved wall 26.The slots 32 regulate the stiffness and curl of the tube 24. Moreparticularly, the size of the slots 32 and spacing of the slots 32 fromone another define the ability of the tube 24 to bend and curl. Theslots 32 in the illustrated embodiment are generally circular or ringshaped. Of course, other shapes for the slots 32 may also be suitable.Moreover, in other embodiments (not shown), the walls 26, 28 of the tube24 may be continuous, i.e., without any slots or other holes, to allowliquids to pass through the tube channel 30.

In the illustrated embodiment, the substrate 22 includes an interconnectregion 34 and an electrode region 36. The interconnect region 34 allowsfor electrical connection of the electrode array 20 with at least oneexternal device (not shown), as described further below.

The substrate 22 of the illustrated embodiment comprises a plurality oflayers of Parylene. That is, several layers of Parylene are connectedtogether to form the substrate 22. Specifically, the substrate 22comprises a first layer 38 of Parylene, also referred to as a base layer38. The first layer 38 is in contact with and affixed to the straightwall 28 of the tube 24.

In the illustrated embodiment, a second layer 40 of Parylene is disposedabove the first layer 34. That is, the second layer 40 is disposed onthe first layer 38 opposite the tube 24. The second layer 40 and thetube 24 are integrally formed as described further below. That is, thesecond layer 40 and tube 24 are comprised of a single unit.

The substrate 22 also supports a plurality of feed lines 42 comprised ofa conductive material. The feed lines 42 of the illustrated embodimentcomprise a metal. More specifically, the feed lines 42 are formed ofchromium-gold-chromium (Cr—Au—Cr). In the illustrated embodiment, thepitch, i.e., the distance between a point on one feed line 42 and acorresponding point on another feed line 42, is about 10 μm. As such, awidth of each feed line 42 is less than 9 μm, to maintain electricalisolation between the feed lines 42.

In the illustrated embodiment, the feed lines 42 are disposed on thesecond layer 40. The feed lines 42 run between the interconnect region34 and the electrode region 36. A third layer 44 of Parylene is disposedabove the feed lines 42 and the second layer 40. That is, the thirdlayer 44 is connected to the second layer 40 opposite the tube 24. Assuch, the feed lines 42 are disposed primarily within the substrate 22,i.e., the feed lines 42 are encased within the substrate 22. As such,the feed lines 42 are insulated by the non-conductive material of thesubstrate 22. Specifically, the third layer 44 of Parylene electricallyinsulates the feed lines 42.

The substrate 22 also supports a plurality of electrodes 46 forconducting electrical energy. The electrodes 46 each comprise anelectrically conductive material, including, but not limited to, ametal. In the illustrated embodiment, the electrodes comprisetitanium-iridium (Ti—Ir). However, in other embodiments, the electrodes46 may be formed of different metals. Furthermore, other electricallyconductive material, such as conductive polymers, could be used to formthe electrodes 46. Moreover, the various electrodes 46 need not beformed of the same type of material and could be formed by a combinationof different materials.

In the illustrated embodiment, the electrodes 46 are supported in theelectrode region 26. Particularly, the electrodes 46 are disposed abovethe third layer 44. At least one electrode 46 is electrically connectedto at least one feed line 42. As the feed lines extend to theinterconnect region 34, the feed lines 42 may electrically connect theelectrodes 46 to the at least one external device. In the illustratedembodiment, each electrode 46 is electrically connected to one feed line42.

The electrode array 20 of the subject invention achieves a high densityof electrodes 46. More specifically, the pitch between the electrodesmay be less than 300 μm. In the illustrated embodiment, as shown in FIG.1, 32 electrodes 46 are supported in the electrode region 26 having alength of about 8 mm. That is, the pitch, or center-to-center spacing,between the electrodes 46 is the illustrated embodiment is about 250 μm.By increasing the density and number of electrodes 46 the electrodearray 20, when used as a cochlear implant, provides improved pitchspecificity over the prior art. Of course, other number of electrodes 46may be achieved as will be realized by those skilled in the art. Duringexperimentation, other electrode arrays 20 (not shown) were fabricatedwith 64 and 128 electrodes 46.

The substrate 22 of the illustrated embodiment includes a fourth layer48 of Parylene disposed above the third layer 44. That is, the fourthlayer is supported by the third layer 44 opposite the tube 24.

The substrate 22 defines a peripheral edge 50 around its periphery. Theelectrode array 20 may include a curl strip 52 disposed adjacent atleast a portion of the peripheral edge 50. The curl strip 52 providesrigidity to the electrode array 20 and further regulates the amount ofbend and/or curl of the array 20. In the illustrated embodiment, thecurl strip 52 is disposed on the fourth layer 48. A fifth layer 54 ofParylene is disposed over the curl strip 52. That is, the fifth layer 54is disposed on the fourth layer 48 opposite the tube 24. As such, thecurl strip 52 is encased within the substrate 22 around the entireperipheral edge 50.

The curl strip 52 of the illustrated embodiment is bimetallic.Specifically, the curl strip 52 is composed of Titanium-Iridium andChromium-Gold (Ti—Ir/Cr—Au). Of course, other materials may be utilizedto form the curl strip 52. Furthermore, the curl strip 52 may be formedof various independent pieces or one continuous piece.

The fourth and fifth layers 48 define a plurality of openings 56. Eachopening 56 encircles at least one electrode 46 to allow electricalcontact with the at least one electrode 46. Preferably, each opening 56encircles just one electrode 46. In the illustrated embodiment, eachopening 56 has a generally circular shape and a diameter less than 200μm. However, other shapes and sizes for the openings 56 may be suitableas realized by those skilled in the art.

The electrode array 20 of the illustrated embodiment providessignificantly greater flexibility than silicon-substrate devices of theprior art and are robust enough to withstand repeated flexing. Testingof the electrode array 20 results in only a 20% impedance drop after6000 cycles of twisting the array 20 to a helical radius of about 2 mm.This testing also revealed that no shorting between the feed lines 42and saline after the 6000 cycles of twisting.

The subject invention also provides an exemplary method of fabricatingthe electrode array 20. However, other methods of fabricating theelectrode array 20 described above may be realized by those skilled inthe art.

Referring to FIG. 2, the method utilizes a carrier wafer 60. The carrierwafer 60 of the illustrated embodiment comprises silicon (Si). Of courseother materials may also be suitable for forming the carrier wafer 60,as realized by those skilled in the art.

The method includes the step of depositing a first composition (notseparately numbered) on the carrier wafer 60 as shown in FIG. 2. Thefirst composition forms the first layer 38 described above. The firstcomposition is preferably a non-conductive material and more preferably,the first composition is a polymer. Most preferably, the firstcomposition is Parylene C and is applied by vapor deposition.

Referring to FIG. 3, a longitudinal slit 62 is defined in the firstlayer 38. In the illustrated embodiment, lithography is utilized todemarcate the area of the slit 62 on the first layer 38. Then, the areaof the first layer 38 is removed using a directional oxygen (O₂) plasmareactive ion etching (RIE) to define the slit 62. Of course, othertechniques for defining the slit 62 may be realized by those skilled inthe art. In the illustrated embodiment, the longitudinal slit 62 has alength of about 16 mm and a width of about 5-20 μm.

The method also includes etching the carrier wafer 60 through thelongitudinal slit 62 to define a channel 64 underneath the first layer38, as shown in FIG. 4. The channel 64 in the carrier wafer 60 isreferred to hereafter as the carrier channel 64. In the illustratedembodiment, the etching of the carrier wafer 60 to form the carrierchannel 64 is accomplished using xenon difluoride. However, thoseskilled in the art realize may realize other suitable techniques forgenerating the carrier channel 64.

In the illustrated embodiment, the maximum depth of the carrier channel64 is about 150-200 μm below a top level of the substrate 60. Saidanother way, the depth of the carrier channel 64 is about 150-200 μmbelow the first layer 38. Of course, other depths may alternatively begenerated. The width of the carrier hannel 64 in the illustratedembodiment is about 100-300 μm. The carrier channel 64 may have agenerally semicircular cross section, as is shown in FIG. 4. However,those skilled in the art realize that the carrier channel 64 may any ofnumerous shapes and sizes.

The method further includes the step of depositing a second composition(not separately numbered). The second composition is preferably anon-conductive material and more preferably, the second composition is apolymer. Most preferably, the second composition is Parylene C and isapplied by vapor deposition.

In the illustrated embodiment, the second composition is depositedthrough the longitudinal slit and around the carrier channel 64 to formthe tube 24 described above having the tube channel 36. The secondcomposition is also deposited above the first layer 38 to form thesecond layer 40 described above. Accordingly, the second compositionseals the longitudinal slit 62. As such, the tube 24 and second layer 40are formed of a unitary material in the illustrated embodiment.

The feed lines 42 are disposed on the second layer 40 opposite the tube24 according to the method. The feed lines 42 are applied to the secondlayer 40 using evaporated metal and lift off.

The method further includes depositing a third composition (notseparately numbered) atop the second layer 40 and the feed lines 42, asshown in FIG. 77. The third composition forms the third layer 44described above. The third composition is preferably a non-conductivematerial and more preferably, the third composition is a polymer. Mostpreferably, the third composition is Parylene C and is applied by vapordeposition. The third layer 44 (as well as the fourth and fifth layers44, 54) acts as insulation to the feed lines 42. A plurality ofapertures 45 are defined in the third layer 44 using directional O₂ RIEor other suitable techniques. Each aperture 45 exposes at least one ofthe feed lines 42.

Referring to FIG. 8, the method continues with the step of disposing aplurality of electrodes 46 on the substrate 22. In the illustratedembodiment, the electrodes are disposed in the apertures 45 such thateach electrode 46 electrically connected to at least one of the feedlines 42. Each electrode 46 in the illustrated embodiment is generallycircular shaped with a diameter of less than 200 μm. Preferably, eachelectrode 46 has a diameter of about 180 μm. Of course, other suitableshapes and sizes for the electrodes 46 will be contemplated by thoseskilled in the art.

In the illustrated embodiment, the electrodes 46 are formed using alift-off technique. More specifically, photoresist (not shown) is placedon the exposed substrate 22, the photoresist is removed from areas wherethe electrodes 46 are to be disposed, the Ti—Ir metal (not shown) isdisposed on the exposed substrate 22 such that the Ti—Ir metal bonds inthe areas where the photoresist has been removed, and acetone (notshown) is applied to the substrate 22. The acetone eats away at theremaining photoresist and removes the Ti—Ir metal, except for theelectrodes 46.

The method also includes the step of depositing a fourth composition(not separately numbered) atop the third layer 40, as shown in FIGS. 9and 10. The fourth composition forms the fourth layer 48 describedabove. The fourth composition is preferably a non-conductive materialand more preferably, the fourth composition is a polymer. Mostpreferably, the fourth composition is Parylene C and is applied by vapordeposition.

The method further includes the step of disposing the curl strip 52 onthe substrate 22. Preferably, the curl strip 52 is disposed adjacent theperipheral edge 50, as shown in FIGS. 11 and 12. After disposition ofthe curl strip 52, a fifth composition (not separately numbered) isdeposited atop the fourth layer 48 and the curl strip 52. The fifthcomposition forms the fifth layer 54 described above. The fifthcomposition is preferably a non-conductive material and more preferably,the fifth composition is a polymer. Most preferably, the fifthcomposition is Parylene C and is applied by vapor deposition.

The method also includes the step of forming the plurality of openings56 in the fourth and fifth layers 48, 52 to expose the electrodes 46.The openings 56 are created using directional O₂ RIE or other suitabletechniques. The openings 56 allow electrical conduction with theelectrodes 46. Preferably, one opening 56 is formed for each electrode46.

The use of five compositions forming five layers 38, 40, 44, 48, 54 isnot absolutely necessary in forming the substrate 22 of the electrodearray 20. Several of these layers 38, 40, 44, 48, 54 could be combinedand/or the compositions applied in combination.

Referring to FIGS. 13 and 14, the method continues with the step ofetching the carrier wafer 60 opposite the substrate 22 to define voids68 with each void 68 exposing an area (not separately numbered) of thetube 24. The creation of the voids 68 is performed using directional RIEor other suitable techniques.

After the voids 68 have been defined in the carrier wafer 60, the methodproceeds with removing the areas of the tube 24 exposed by the voids 68to define the slots 32 within the tube 24. The slots 32 are generatedusing oxygen plasma.

The method further includes the step of releasing the tube 24 andsubstrate 22 from the carrier wafer 60. In the illustrated embodiment,the tube 24 and substrate 22 are released from the carrier wafer 60 bydissolving the carrier wafer 60 using a solution including potassiumhydroxide (KOH). Preferably, the solution is about 2% KOH. However,other techniques may be implemented as realized by those skilled in theart.

FIGS. 16 and 17 show cross sectional views of the electrode array 20after release from the carrier wafer 60. Furthermore, FIG. 18 shows aperspective view of a portion of the electrode array 16 and FIG. 19shows a close up top view of two electrodes 46 and a plurality of feedlines 42.

Curl may be induced into the electrode array 20 by utilizing a wire 74.The wire 74 is disposed through the tube channel 30 to hold the array 20in a curled position.

The electrode array 20 provides high electrode 46 density, built incurl, integrated positioning, and tailored stiffness for use as part ofthe cochlear implant. The substrate 22 is flexible and robust enough towithstand the tight helical pitch of the cochlea. This substrate 22 canhug the modiolus of the cochlear for close proximity to neuralreceptors. The size and spacing of the openings 56 can be altered tomake the array stiff enough for insertion in the cochlea yet pliableenough to curl. The openings 56 also provide a lumen where a stylet wire(not shown) can be advanced to straighten the array for insertion intothe cochlea and then fed off the array to allow it to curl into thecochlea. Alternatively, a microelectromechanical systems (MEMS) solutionmay be implemented to perform insertion of the electrode array 20 intothe cochlea.

The electrode array 20 may also find application as part of a neuralprobe (not shown). Polymer neural probes are of increasing interestbecause they more closely match the tissue compliance then hardersilicon or glass probes. This match in compliance improves thesynchronicity of probe motion with that of the tissue, so that theprobes do not tear through the tissue in response to micro motions.However, the typical drawback of polymer probes is that they are highlyflexible and need to be strengthened with stiffeners in order topenetrate the brain tissue.

The electrode array 20 may also find application with for dispensingcell growth promoters or pharmaceuticals to the surrounding tissuethrough the tube channel 30, either with or without the slots 32. Thetube channel(s) 30 beneath the electrodes 20 may be used to deliverother fluid locally to surrounding cells. Electrochemical reactions canbe studied locally, by stimulating cells chemically and recording theelectrical response via the electrodes 46. Alternatively oradditionally, the electrodes 46 may be used to electrically stimulatecells.

Prior art polymer electrode arrays have been designed with drug deliverychannels. However, the channels were fabricated using sacrificialphotoresist. The photoresist is sandwiched between two polymer layerssuch that when it is dissolved away it leaves an empty space (channel)in the polymer. The sacrificial process of the prior art has thedrawback of limiting the cross-sectional dimensions of the channel tothe maximum thickness the resist can be spun on, typically less than 100μm. In comparison, the cross-sectional dimensions of the tube channel 30of the present invention are only limited by the thickness of thecarrier wafer 64, thus providing cross-sectional dimensions up to about500 μm. Furthermore, these cross-sectional dimensions can even beextended beyond that through bonding of carrier wafers 64.

The present invention has been described herein in an illustrativemanner, and it is to be understood that the terminology which has beenused is intended to be in the nature of words of description rather thanof limitation. Obviously, many modifications and variations of theinvention are possible in light of the above teachings. The inventionmay be practiced otherwise than as specifically described within thescope of the appended claims.

1.-7. (canceled)
 8. An electrode array comprising: a tube having atleast one wall defining a channel; a substrate comprised ofnon-conductive material and supported at least partially by the tube; aplurality of electrodes comprised of a conductive material and supportedby the substrate; and a plurality of feed lines comprised of aconductive material and disposed primarily within the substrate whereineach feed line is electrically connected to at least one of theplurality of electrodes; wherein the at least one wall of the tube iscontinuous to allow liquids to pass through the tube channel.
 9. Anelectrode array as set forth in claim 8 wherein the tube comprisesParylene.
 10. An electrode array as set forth in claim 8 wherein thetube comprises a metal.
 11. An electrode array as set forth in claim 8wherein the substrate defines a peripheral edge and the electrode arrayfurther comprises a curl strip disposed adjacent at least a portion ofthe peripheral edge.
 12. An electrode array as set forth in claim 11wherein the curl strip is bimetallic.
 13. An electrode array as setforth in claim 8 wherein the electrodes comprise metal.
 14. An electrodearray as set forth in claim 8 wherein the substrate includes a firstlayer of a polymer supported at least partially by the tube and at leastone insulating layer of a polymer disposed on the base layer oppositethe tube.
 15. An electrode array as set forth in claim 14 wherein saidat least one insulating layer comprises a second layer disposed on thefirst layer opposite the tube and a third layer disposed on the secondlayer opposite the tube.
 16. An electrode array as set forth in claim 15wherein the feed lines are disposed between the first layer and thesecond layer.
 17. An electrode array as set forth in claim 16 whereinthe electrodes are disposed between the second layer and the thirdlayer.
 18. An electrode array as set forth in claim 8 wherein each ofsaid electrodes has a generally circular shape and a diameter less than200 μm and a pitch between electrodes of less than 300 μm.
 19. Anelectrode array comprising: a tube comprised of Parylene and having atleast one wall defining a channel; a substrate comprised ofnon-conductive material and supported at least partially by the tube; aplurality of electrodes comprised of a conductive material and supportedby the substrate; and a plurality of feed lines comprised of aconductive material and disposed primarily within the substrate whereineach feed line is electrically connected to at least one of theplurality of electrodes.
 20. An electrode array as set forth in claim 19wherein a pitch between electrodes is less than 300 μm.
 21. An electrodearray as set forth in claim 19 wherein the at least one wall of the tubeincludes one or more slots that regulate the stiffness and curl of thetube.
 22. An electrode array as set forth in claim 8 wherein the atleast one wall of the tube includes one or more slots that regulate thestiffness and curl of the tube.
 23. An electrode array as set forth inclaim 22 wherein the size of the slots define the ability of the tube tobend and curl.
 24. An electrode array as set forth in claim 22 whereinthe spacing of the slots relative to one another define the ability ofthe tube to bend and curl.
 25. An electrode array as set forth in claim22 wherein the size of the slots and the spacing of the slots relativeto one another define the ability of the tube to bend and curl.